Flow rate range variable type flow rate control apparatus

ABSTRACT

A pressure type flow rate control apparatus is provided wherein flow rate of fluid passing through an orifice is computed as Qc=KP1 (where K is a proportionality constant) or as Qc=KP2 m (P1−P2) n  (where K is a proportionality constant, m and n constants) by using orifice upstream side pressure P1 and/or orifice downstream side pressure P2. A fluid passage between the downstream side of a control valve and a fluid supply pipe of the pressure type flow rate control apparatus comprises at least 2 fluid passages in parallel, and orifices having different flow rate characteristics are provided for each of these fluid passages, wherein fluid in a small flow quantity area flows to one orifice for flow control of fluid in the small flow quantity area, while fluid in a large flow quantity area flows to the other orifice for flow control of fluid in the large flow quantity area.

FIELD OF THE INVENTION

The present invention relates to a flow rate control apparatus with a fluid supply system used for semiconductor manufacturing facilities, chemical products manufacturing facilities, pharmaceutical products manufacturing facilities, food products manufacturing facilities, and the like. More particularly, the present invention relates to a flow rate range variable type flow rate control apparatus with which both the expansion of a flow rate control range and the maintenance of high control accuracy can be easily achieved with a pressure type flow rate control apparatus and a thermal type mass flow rate control apparatus.

BACKGROUND OF THE INVENTION

Not only high flow rate control accuracy is required for a flow rate control apparatus used with semiconductor manufacturing facilities and the like but also a considerably wide control range is required with regard to the flow rate control range.

As a flow rate control range becomes wider, it is inevitable that the control accuracy is lowered in a low flow rate area, thus making it difficult to make up for a degradation of a control accuracy in a low flow rate area only with a feature to correct a measured value provided with a flow rate control apparatus.

To overcome this problem, in a general way a flow rate control range is divided into a plurality of flow rate areas, e.g. the area for a large flow quantity, the area for a medium flow quantity and the area for a small flow quantity to meet a required flow rate control range, and thus providing 3 sets of flow rate control apparatus responsible for the flow rate control of each flow rate area in parallel so that the high flow rate control accuracy can be maintained over the wide flow rate control range.

However, with a system for which a plurality of devices responsible for different flow rate control ranges respectively are provided in parallel, it becomes unavoidable that installation costs go up, which makes it difficult to reduce the installation costs. At the same time, switching operation of flow rate control apparatuses becomes time-consuming and troublesome.

Also, with semiconductor manufacturing facilities, a pressure type flow rate control apparatus has become more popular these days replacing a conventional thermal type mass flow rate control apparatus.

The reason is that a pressure type flow rate control apparatus is not only simple in structure, but also has excellent properties in responsiveness, control accuracy, control stabilities,manufacturing costs, maintainability, and the like. Furthermore, it can be easily replaced with a thermal type mass flow rate control apparatus.

FIG. 7(a) and FIG. 7(b) illustrate one example of a basic constitution of the afore-mentioned conventional pressure type flow rate control apparatus FCS. The major portion of a pressure type flow rate control apparatus FCS comprises a control valve 2, pressure detector, 6, 27, an orifice 8, flow rate computation circuits 13, 31, a flow rate setting circuit 14, a computation control circuit 16, a flow rate output circuit 12, and the like.

In FIG. 7(a) and FIG. 7(b), 3 designates an orifice upstream side pipe, 4 a valve driving part, 5 an orifice down, stream side pipe, 9 a valve, 15 a flow rate conversion circuit, 10, 11, 22, 28 amplifiers, 7 a temperature detector, 17, 18, 29 A/D converters, 19 a temperature correction circuit, 20, 30 computation circuits, 21 a comparison circuit, Qc a computation flow rate signal, Qf a switching computation flow rate signal. Qe a flow rate setting signal. Qo a flow rate output signal, Qy a flow rate control signal, P₁ orifice upstream side gas pressure. P₂ orifice downstream side gas pressure, and k a flow rate conversion rate.

The afore-mentioned pressure type flow rate control apparatus FCS in FIG. 7(a) is mainly used either in case the ratio P₂/P₁ of the orifice upstream side gas pressure P₁ and the orifice downstream side gas pressure P₂ is equal to the critical value of a fluid or in case it is lower than the critical value (that is, when a gas flow is constantly under the critical state). The gas flow rate Qc passing through an orifice 8 is given by Qc=KP₁ (where K is a proportionality constant).

The afore-mentioned pressure type flow rate control apparatus FCS in FIG. 7(b) is mainly used for the flow rate control of gases to be in the flow condition in both the critical and non-critical states. The flow rate of a gas passing through an orifice is given by Qc=KP₂ ^(m)(P₁−P₂)^(n) (where K is a proportionality constant, m and n are constants).

With the afore-mentioned pressure type flow rate control apparatus in FIG. 7(a) and FIG. 7(b), the setting value of a flow rate is given by a voltage value as Qe a flow rate setting signal. For example, assuming that the pressure control range 0˜3 (kgf/cm² abs) of the upstream side pressure P₁ is expressed by the voltage range 0˜5V, Qe=5V (full scale value) becomes equivalent to the flow rate Qc=KP₁ at the pressure P₁ of 3 (kgf/cm² abs).

For example, when the conversion rate k of a flow rate conversion circuit 15 is set at 1, a switching computation flow ate signal Qf (Qf=kQc) becomes 5V if a flow rate setting signal Qe=5V is inputted, thus a control valve 2 is operated for opening and closing until the upstream side pressure P₁ becomes 3 (kgf/cm² abs), to allow the gas of a flow rate Qc=KP₁ corresponding to P₁=3 (kgf/cm² abs) to flow through an orifice 8.

In case that the pressure range to control is switched to 0˜2 (kgf/cm² abs) and the pressure range is expressed by a flow rate setting signal Qe of 0˜5(V) (that is, when a full scale value 5V gives 2 (kgf/cm² abs)), the afore-mentioned flow rate conversion rate k is set at 2/3.

As a result, if a flow rate setting signal Qe=5(V) is inputted, a switching computation flow rate signal Qf becomes Qf=5×2/3(V) because of Qf=kQc, thus a control valve 2 is operated for opening and closing until the upstream side pressure P₁ becomes 3×2/3=2 (kgf/cm² abs).

Namely, a full scale flow rate is converted so that Qe=5V expresses a flow rate Qc=KP₁ equivalent to P₁=2 (kgf/cm² abs).

Under a critical condition, a flow rate Qc of a gas passing through an orifice 8 is given by the afore-mentioned equation Qc=KP₁. However, when a type of gas which flow rate is to be controlled changes, the afore-mentioned proportionality constant K changes if the same orifice 8 is in use.

It is also same with the afore-mentioned pressure type flow rate control apparatus in FIG. 5(b). A flow rate Qc of a gas passing through an orifice 8 is given by Qc=KP₂ ^(m)(P₁−P₂)^(n) (where K is a proportionality constant, and m and n are constants). When a type of gas changes, the afore-mentioned proportionality constant K also changes.

[Patent Document 1] TOKU-KAI-HEI No. 8-338546 Public Bulletin

[Patent Document 2] TOKU-KAI No. 2000-66732 Public Bulletin

[Patent Document 3] TOKU-KAI No. 2000-322130 Public Bulletin

[Patent Document 4] TOKU-KAI No. 2003-195948 Public Bulletin

[Patent Document 5] TOKU-KAI No. 2004-199109 Public Bulletin

OBJECTS OF THE INVENTION

With a pressure type flow rate control apparatus, especially with an apparatus which employs the method with which computation control is performed as a flow rate Qc=KP₁ under the critical state as shown in FIG. 5(a), a flow rate control range becomes gradually narrower as an orifice secondary side P₂ (that is, a chamber and the like to which a gas is supplied) rises. The reason for that is that because an orifice primary side pressure P₁ is controlled at a certain pressure value complying with a flow rate setting value, it is inevitable that the correction range of an orifice primary side pressure P₁, that is, the control range of a flow rate Qc by means of P₁ becomes narrower as an orifice secondary side pressure P₂ rises under the conditions in which P₂/P₁ satisfies the critical expansion conditions.

The flow state of a fluid falling outside the afore-mentioned critical state makes the accuracy of a flow rate control substantially reduced. As a result, unevenness in quality is caused with semiconductor products.

In other words, with a pressure type flow rate control apparatus wherein a flow rate control of a fluid is conducted under a critical state, the range possible to achieve the flow rate control is substantially narrowed in comparison with those of a conventional thermal type mass flow rate control apparatus or so-called differential pressure type flow rate control apparatus.

As a result, manufacturing costs of semiconductor manufacturing facilities and the like go up due to the reason that two pressure type flow rate control apparatuses having different flow rate control ranges are required.

The present invention is to solve the afore-mentioned problems with a conventional flow rate control apparatus, that is, (a) a difficulty in reducing costs of a flow rate control apparatus because it becomes necessary that a plurality of flow rate control apparatus having different flow rate ranges are installed in parallel to secure a prescribed control accuracy in the case that a wide flow rate control range is required and thus being used in the manner of switching them, and (b) another problem is that with a pressure type flow rate control apparatus which is basically used for a flow rate control under a critical condition, a flow rate control range is gradually reduced along with the pressure rise on the orifice secondary side, thus a plurality of flow rate control apparatuses having different flow rate ranges being required to deal with the matter. It is an primary object of the present invention to provide a flow rate range variable type flow rate control apparatus, which makes it possible that a highly accurate flow rate control of a fluid is achieved over a wide flow rate control range only with one set of an apparatus by means of switching and controlling fluid passages inside the flow rate control apparatus.

Disclosure of the Invention

To overcome difficulties with the afore-mentioned invention, the present invention as claimed in Claim 1 is basically so constituted that a flow rate is controlled by means of switching a fluid in a large flow quantity area and a fluid in a small flow quantity area in the manner that fluid passages to a flow rate detection part of the flow rate control apparatus are installed at least for a small flow quantity and a large flow quantity, making a fluid in a small flow quantity area flow to a flow detect on part through the afore-mentioned fluid passage for a small flow quantity, to switch the detection level of a flow rate control part to the detection level suitable for the detection of a small flow rate area and also making a fluid in the large flow quantity area flow to a flow detection part through the afore-mentioned fluid passage for a large flow quantity, to switch the detection level suitable for the detection of a large flow quantity area.

Also, to overcome difficulties with the afore-mentioned invention, the present invention as claimed in Claim 2 is basically so constituted that with a pressure type flow ate control apparatus wherein a flow rate of a fluid passing through an orifice 8 is computed as Qc=KP₁ (where K is a proportionality constant) or as Qc=KP₂ ^(m)(P₁−P₂)^(n) (where K is a proportionality constant, m and n constants) by using an orifice upstream side pressure P₁ and/or an orifice downstream side pressure P₂, a fluid passage between the downstream side of a control valve and a fluid supply pipe of said pressure type flow rate control apparatus are made to be more than at least 2 fluid passages in parallel, orifices having different flow rate characteristics are provided with the afore-mentioned fluid passages arranged in parallel, the afore-mentioned fluid in a small flow quantity area is made to flow to one orifice for the flow control of the fluid in a small flow quantity area, and the fluid in a large flow quantity area is made to flow to the other one for the flow control of the fluid in a large flow quantity area.

The present invention as claimed in Claim 3 according to Claim 2 is so constituted that the number of fluid passages arranged in parallel are made to be 2, and two orifices, one for a large flow quantity and the other for a small flow quantity, are provided, and thus the control range of a fluid's flow rate is switched either to a small flow quantity area or to a large flow quantity area by means of operating a switching valve installed on the fluid passage of the orifice for a large flow quantity.

The present invention as claimed in Claim 4 according to Claim 2 is so constituted that 3 different orifices, an orifice for a large flow quantity, an orifice for a medium flow quantity and an orifice for a small flow quantity, are made, and No. 1 switching valve. No. 2 switching valve and an orifice for a large flow quantity are provided on one fluid passage in series, while an orifice for a small flow quantity and an orifice for a medium flow quantity are provided on the other fluid passage, and furthermore, the passage for communication with between the afore-mentioned 2 switching valves and the passage for communication with between an orifice for a small flow quantity and an orifice for a medium flow quantity are made to be for communication each other.

The present invention as claimed in Claim 5 according to Claim 2 is so made that a fluid flowing through an orifice of a pressure type flow rate control apparatus is made to be a fluid under a critical condition.

Furthermore, to overcome difficulties with the afore-mentioned invention, the present invention as claimed in Claim 6 is basically so constituted that with a thermal type mass flow rate control apparatus comprising a flow rate control valve, a laminar flow element device part, a flow rate sensor part, and the like, wherein temperature changes in proportion to a mass flow rate of a fluid are detected at the flow rate sensor part, and a fluid with a certain set flow rate is made to flow out by means of opening/closing a flow rate control valve based on said detected temperature, a fluid passage to a flow rate control valve is made to be more than at least 2 fluid passages arranged in parallel, both laminar flow elements with different coarseness and flow rate sensors are provided with the afore-mentioned fluid passages in parallel, the afore-mentioned fluid in a small flow quantity area is made to flow to one laminar flow element for a flow rate control of a fluid in a small flow quantity area, while the afore-mentioned fluid in a large flow quantity area is made to flow to the other laminar flow element for a flow rate control of a fluid in a large flow quantity area.

The present invention as claimed in Claim 7 according to Claim 6 is so constituted that the number of fluid passages in parallel are made to be 2, two laminar flow elements are made to be a coarse laminar flow element for a large flow quantity and a fine laminar flow element for a small flow quantity, and the control range of a fluid flow rate is switched either to a small flow quantity area or to a large flow quantity area by means of operating switching valves respectively provided on both fluid passages.

Effect of the Invention

The present invention is so constituted that a flow rate is controlled in the manner that a flow rate control is performed by appropriately combining an orifice 8 c for a large flow quantity, an orifice 8 a for a small flow quantity (or an orifice 8 c for a large flow quantity, an orifice 8 b for a medium flow quantity and an orifice 8 a for a small flow quantity), thus making it possible that a highly accurate flow rate control is achieved over a wide flow rate range with an error of less than 1% set point.

Also, the present invention makes the operation simple because a flow rate control area can be automatically selected by operating a switching valve.

Furthermore, the present invention can be applied to a flow rate control of various kinds of fluid supply facilities because of easy changes of a type of gases by making use of a flow factor F.F. in the case that a flow rate control of a fluid under a critical condition is basics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a flow rate range variable type flow rate control apparatus according to the embodiment 1.

FIG. 2 is a chart to show flow rate characteristics of a flow rate control apparatus in FIG. 1.

FIG. 3 is a block diagram of a flow rate range variable type flow rate control apparatus according to the embodiment 2.

FIG. 4 is a chart to show flow rate characteristics of a flow rate control apparatus in FIG. 3.

FIG. 5 shows an example of flow rate control characteristics of a pressure type flow rate control apparatus FCS outside the range of a critical condition.

FIG. 6 is a block diagram of a flow rate range variable type flow rate control apparatus according to the embodiment 3.

FIG. 7 is an explanatory drawing to show a basic constitution of a conventional pressure type flow rate control apparatus.

LIST OF REFERENCE NUMBERS AND CHARACTERS

FCS pressure type flow rate control apparatus

MFC thermal type mass flow rate control apparatus

1 control part

2 control valve

3 orifice primary side pipe

4 driving part

5 fluid supply pipe

6 pressure sensor

8 a orifice for a small flow quantity

8 b orifice for a medium flow quantity

8 c orifice for a large flow quantity

32 No. 1 switching electro-magnetic valve

33 No. 2 switching electro-magnetic valve

34 No. 1 switching valve

34 a valve driving part

34 b proximity sensor

35 No. 2 switching valve

35 a valve driving part

35 b proximity sensor

36 control part

36 a bridge circuit

37 flow rate control valve

38, 38 a, 38 b laminar flow element bypasses

39 flow rate sensor part

40 a, 40 b fluid passages

41, 42 switching valves

BEST MODE OF CARRYING OUT THE INVENTION Embodiment 1

Referring to the drawings, embodiments of the present invention are described hereunder.

FIG. 1 is a block diagram of a flow rate range variable type according to the embodiment 1 of the present invention. In FIG. 1, 1 designates a control part, 2 a control valve, 3 an orifice upstream side (primary side) pipe, 4 a valve driving part, 5 a fluid supply pipe, 6 a pressure sensor, 8 a an orifice for a small flow quantity, 8 b an orifice for a medium flow quantity, 8 c an orifice for a large flow quantity, 32, 33 switching electro-magnetic valves, and 34, 35 switching valves.

A control part 1, a control valve 2, a valve driving part 4, a pressure sensor 6, and the like of the afore-mentioned pressure type flow rate control apparatus have been disclosed. With a control part, there are provided flow rate input/output signal (an input signal of a set flow rate, an output signal of a controlled flow rate·DC 0-5V) terminals Qe, Qo, a power supply terminal (_DC 15V) E, and input terminals S_(L), S_(M), S_(s) for a controlled flow rate switching command signal.

The afore-mentioned switching electro-magnetic valves 32, 33 which have been disclosed are air operation type electro-magnetic valves. When switching signals C₁, C₂ are inputted from a control part 1, a driving gas (0.4˜0.7 MPa) Gc is supplied so that switching electro-magnetic valves 32, 33 start working, thus a driving gas Gc is supplied to valve driving parts 34 a, 35 a of switching valves, and switching valves 34, 35 start operating for opening and closing.

Furthermore, operation of both switching valves 34, 35 are detected by proximity switches 34 b, 35 b installed on valve driving parts 34 a, 35 a, and inputted to a control part 1.

With present embodiments, a pneumatically operated normally closed type valve has been employed as switching valves 34, 35.

Pipes 5 a, 5 b, 5 c, 5 d, 5 e 5 f in FIG. 1 form bypass passages of orifices 8 a, 8 b, 8 c. When a flow rate to be controlled is in a small flow quantity area, a fluid which flow rate is controlled with an orifice 8 a for a small flow quantity flows mainly through pipes 5 b, 5 d, 5 c, 5 e.

When a flow rate to be controlled is in a medium flow quantity area, a fluid flows in an orifice 8 b for a medium flow quantity through pipes 5 a, 5 b, 5 d, and a fluid which flow rate is controlled mainly with an orifice 8 b for a medium flow quantity flows out into a fluid supply pipe 5.

Furthermore, when a flow rate to be controlled is in a large flow quantity area, a fluid flow out to an orifice 8 c for a large flow quantity through a pipe 5 a, and a fluid which flow ate is controlled mainly with an orifice 8 c for a large flow quantity flow in a fluid supply pipe 5.

More concretely, in the case that the maximum flow rate to be controlled is, for example, 2000 SCCM, an orifice for the maximum flow rate of 20 SCCM is employed as an orifice 8 a for a small flow quantity, an orifice for the maximum flow rate of 200 SCCM is employed as an orifice 8 b for a medium flow quantity, and an orifice for the maximum flow quantity of 1780 SCCM is employed as an orifice 8 c for a large flow quantity respectively.

Namely, in the case that a flow rate is controlled for a small flow quantity less than 20 SCCM, a switching signal Ss is inputted to a control part, a driving gas Gc is sent to No. 2 switching valve 35 by releasing No. 2 electro-magnetic switching valve 33, and said No. 2 switching valve 35 is released (while No. 1 switching valve 34 is maintained in a state of closing).

As a result, a fluid flows to a pipe 5 through a pipe 3, an orifice 8 a for a small flow quantity, a pipe 5 b, a valve 35, an orifice 8 c for a large flow quantity, a pipe 5 c and a pipe 5 d, an orifice 8 b for a medium flow quantity, and a pipe 5 f, thus the flow rate Q_(L) of the fluid being controlled as Q=K_(L)P₁ (where K_(L) is a constant specific to an orifice 8 a for a small flow quantity).

Also, its flow rate characteristics are shown by characteristic A in FIG. 2. A flow rate control can be performed with accuracy of an error of less than ±1% set point over the flow rate range of 20˜2 SCCM.

In the case that the flow rate to be controlled is 200 SCCM (for the approximately medium flow quantity), No. 1 switching valve 34 is switched to the state of opening and No. 2 switching valve 35 is switched to the state of closing, and a fluid is made to flow to an orifice 8 b for a medium flow quantity through a pipe 3, a pipe 5 a, a valve 34, a pipe 5 b and a pipe 3, and an orifice 8 a for a small flow quantity, thus the flow rate Q_(M) of the fluid being controlled as Q=K_(M)P₁ (where K_(M) is a constant specific to an orifice 8 b for a medium flow quantity).

Its flow rate characteristics are shown by characteristics B in FIG. 2. A flow rate control can be performed with accuracy of an error of less than ±1% set point over the flow rate range of 200˜20 SCCM.

Furthermore, in the case that a flow rate to be controlled is 2000 SCCM (the maximum flow ate), both switching valves 34, 35 are released through the mediation of both switching electro-magnetic valves 32, 33, and a fluid is supplied to a pipe 5 through a pipe 3, a pipe 5 a, a valve 34, a valve 35, an orifice 8 c for a large flow quantity, a pipe 5 c and an orifice 8 a for a small flow quantity, an orifice 8 b for a medium flow quantity, a pipe 5 f.

In this case, a flow rate of the fluid is controlled mainly with an orifice 8 c for a large flow quantity as a flow rate Q_(M)=K_(M)P₁ (where K_(M) is a constant specific to an orifice 8 c for a large flow quantity). However, strictly speaking, a flow rate of a pipe 5 is controlled as a sum of the flow rate Q_(M)=K_(M)P₁ passing through an orifice 8 b for a medium flow quantity and the flow rate Q_(L)=K_(L)P₁ passing through an orifice 8 c for a large flow quantity.

Also, in this case, flow rate characteristics are shown by characteristics C in FIG. 2. The flow rate a can be controlled with accuracy of an error of less than ±1% set point over the flow rate range of 2000˜200 SCCM.

Embodiment 2

FIG. 3 shows the embodiment 2 of the present invention, wherein a flow rate control is appropriately performed by employing an orifice 8 a for a small flow quantity and an orifice 8 c for a large flow quantity.

For example, in the case that a flow rate control for a maximum flow rate of 2000 SCCM is performed, it is so constituted that a flow rate up to 200 SCCM is controlled with an orifice 8 a for a small flow quantity and a flow rate up to 2000 SCCM is controlled with an orifice 8 c for a large flow quantity.

Concretely, in the case that a flow rate up to 200 SCCM is controlled, a switching valve 34 is maintained in a state of closing, and a flow rate Q_(S) of a fluid passing through an orifice 8 a for a small flow quantity is controlled as Q_(S)=K_(S)P₁ (where K_(s) is a constant specific to an orifice 8 a).

By using said orifice 8 a for a small flow quantity, the flow rate can be controlled with accuracy of an error of less than ±1% set point over the flow rate range of 2000 SCCM˜20 SCCM.

Characteristics D in FIG. 4 shows the flow rate control characteristics at this time. In the case that a pipe 5 on the orifice downstream side is less than 100 Torr, it has been verified that an error can be reduced to less than ±1% set point with a flow rate of 20 SCCM.

With the afore-mentioned flow rate control method in FIG. 3, if an orifice downstream pressure exceeds 100 Torr, or if an flow rate Qs of a fluid is found to be less than 20 SCCM though the orifice downstream side pressure is less than 1000 Torr, it becomes difficult to maintain the flow rate control error to be less than ±1% set point.

Accordingly, in such a case, the flow rate range of less than 20 SCCM is controlled in the manner of a so-called pulse control as shown in FIG. 4.

A pulse control mentioned herewith is a control method wherein a fluid is made to flow into a pipe 3 in the pulse form by performing the opening and closing of a control valve 2 on the orifice upstream side with pulse signals so that the flow rate of a fluid passing through an orifice 8 a for a small flow quantity can be controlled with comparatively high accuracy by means of adjusting the pulse number of opening and closing.

On the other hand, to control a fluid of the flow rate of less than 2000 SCCM, a switching valve 34 is released through the mediation of a switching electro-magnetic valve 32, thus the fluid being made to flow to a pipe 5 through a pipe 5 a, a switching valve 34, an orifice 8 c for a large flow quantity, an orifice 8 a for a small flow quantity, and a pipe 5 g.

Namely, the flow rate of a fluid flowing into a pipe 5 is the sum of the flow rate Qc=KcP₁ passing through an orifice 8 c for a large flow quantity (where Kc is a constant specific to an orifice 8 c for a large flow quantity) and the flow rate Qs=KsP₁ passing through an orifice 8 a for a small flow quantity (where Ks is a constant specific to an orifice 8 a for a small flow quantity). The curvature of flow rate characteristics is as shown by characteristics E in FIG. 4.

As described above, with the embodiment 1 and the embodiment 2 of the present invention, the flow rate control with accuracy of an error of less than ±1% set point becomes possible over the wide flow rate control range of, for example, 2000 SCCM˜2 SCCM by means of appropriately combining an orifice 8 c for a large flow quantity and an orifice 8 a for a small flow quantity (or an orifice 8 c for a large flow quantity, an orifice 8 b for a medium flow quantity and an orifice 8 a for a small flow quantity).

A swift switching operation is required to change the flow rate of a gas when a flow rate control is performed with an orifice 8 a for a small flow quantity. In such a case, with the present invention, the pressure drop time of a pipe on the orifice secondary side can be easily shortened in the manner of installing bypass passages (5 a, 34, 8 c, 5 c) in parallel with a flow passage of an orifice 8 a, and releasing said bypass passages.

Furthermore, with the embodiment 1 and the embodiment 2 of the present invention, for the reason that it is so constituted that the flow rate control of a fluid is performed under a critical condition, a computed flow rate can be converted to the flow rate of a gas in use by making use of a so-call d flow factor F.F. even when a type of gas is altered, thus making it possible that excellent properties of a pressure type flow rate control apparatus are fully utilized.

Accuracy of a flow rate control in a state outside a critical condition of a fluid with a pressure type flow rate control apparatus used in the embodiment 1 and the embodiment 2 is shown in FIG. 5 by making an orifice secondary side pressure P₂ as a parameter. For example, as shown by curvature F, in the case of P₂=100 Torr, the error exceeds 1% F.S. at a point that the flow rate to be controlled reaches approximately 5% of a rated set flow rate.

As a result, as shown by characteristics D (200 SCM˜20 SCCM with an orifice 8 a for a small flow quantity) in FIG. 4, a flow rate control can be performed surely with accuracy of an error of less than ±1% set point between 200 SCCM˜20 SCCM. However, when a flow rate to be controlled comes to less than 20 SCCM, it becomes practically difficult to lower an error of surely less than 1% F.S. to the point of the approximate flow rate 5% (200 SCCM×5%=10 SCCM) of the set flow rate because when a flow rate to be control comes to be less than 20 SCCM, it comes out of a critical condition at a time of an orifice secondary side pressure P₂ being 100 Torr.

Accordingly, as shown in FIG. 4, in the case of a small flow quantity area (20 SCCM˜10 SCCM) of 10%˜5% of the set flow ate, a pulse control method can be employed. (Of cause, there is no need to employ the method because an error of less than 0.1% F.S. (when a full scale of an orifice for a large flow quantity is used as a standard) can be maintained.)

Embodiment 3

FIG. 6 shows the embodiment 3 of the present invention wherein a so-called thermal type mass flow rate control apparatus MFC is employed for a flow rate control apparatus.

As shown in FIG. 6, said thermal type mass flow rate control apparatus comprises a control part 36, a flow rate control valve 37, a laminar flow element bypass part 38, a flow rate sensor part 39, a switching valve 40, and the like. Temperature changes in proportion to a mass flow rate of a fluid are detected with a flow rate sensor part 39, and a fluid of a certain set flow rate is made to flow out by means that a flow rate control valve 37 is controlled for opening and closing based on said detected temperature.

A thermal type mass flow rate control apparatus MFC itself has been disclosed. Therefore, detail description is omitted herewith.

In FIG. 6, 36 a designates a bridge circuit, 36 b an amplification circuit, 36 c a correction circuit, 36 d a comparison circuit, 36 e a valve driving circuit and 36 f an actuator.

With the embodiment 3 of the present invention, 2 passages 40 a, 40 b are separately installed as a bypass passage of a laminar flow bypass part 38, and switching valves 41, 42 are provided on the passages respectively.

Namely, a coarse laminar element 38 a is provided with one fluid passage 40 a of a bypass passage which is used for a flow rate control of a fluid with a medium flow quantity, while a coarser laminar element 38 b is provided with the other fluid passage 40 b of a bypass passage which is used for a flow rate control of a fluid with a large flow quantity.

Concretely, a switching valve 41 and a switching valve 42 are made open to control a flow rate of a fluid with a large flow quantity.

A switching valve 42 and a switching valve 41 are made closed to control a flow rate of a fluid with a small flow quantity, and the amplification level of an amplification circuit 36 b of a control part 36 is switched to the level suitable for detecting a small flow quantity.

Furthermore, a switching valve 41 is made closed and a switching valve 42 is made open to control a flow rate of a fluid with a medium flow quantity, and the amplification level and the like of the afore-mentioned amplification circuit 36 b is switched to the level suitable for detecting a medium flow quantity.

Accordingly, a highly accurate flow rate control becomes possible over 3 flow rate ranges of large, medium and small flow quantities by using one set of thermal type mass flow rate control apparatus MFC wherein the afore-mentioned switching valves 41, 42 are switched and the amplification level of a control part 36 and the like are also switched.

FEASIBILITY OF INDUSTRIAL USE

The present invention can be applied to fluid supplying facilities for various kinds of fluid used with industries such as semiconductor manufacturing, chemical goods manufacturing, pharmaceutical products manufacturing, foods processing and the like. 

1-7. (canceled)
 8. A flow rate range variable type flow rate control apparatus comprising: (a) a thermal type mass flow rate control apparatus comprising (i) a flow rate control valve connected to a first fluid passage; (ii) a laminar flow element device part disposed on the first fluid passage; and (iii) a flow rate sensor part, wherein temperature changes in proportion to a mass flow rate of fluid are detected at the flow rate sensor part, and fluid with a predetermined set flow rate is made to flow out by opening or closing the flow rate control valve based on detected temperature of fluid flowing in the first fluid passage; and (b) a second fluid passage to the flow rate control valve that comprises at least one third fluid passage arranged in parallel, wherein the at least one third fluid passage is provided with a laminar flow element and a switching valve, wherein the laminar flow element has a different coarseness from the other, and fluid flowing in a small flow quantity range is made to flow to one laminar flow element that controls flow rate of fluid flowing in the small flow quantity range while fluid flowing in the large flow quantity range is made to flow to the other laminar flow element that controls flow rate control of fluid flowing in the large flow quantity range; and.
 9. A flow rate range variable type flow rate control apparatus as claimed in claim 8, wherein two third fluid passages are arranged in parallel, and the corresponding two laminar flow elements include a coarse laminar flow element for large flow quantity and a fine laminar flow element for small flow quantity, and a control range of fluid flow rate is switched either to the small flow quantity range or to the large flow quantity range by operating switching valves respectively provided on each third fluid passage.
 10. A flow rate range variable type flow rate control apparatus comprising: (a) a thermal type mass flow rate control apparatus comprising (i) a flow rate control valve connected to a first fluid passage; (ii) a laminar flow element device part disposed on the first fluid passage; and (iii) a flow rate sensor part, wherein temperature changes in proportion to a mass flow rate of fluid are detected at the flow rate sensor part, and fluid with a predetermined set flow rate is made to flow out by opening or closing the flow rate control valve based on detected temperature of fluid flowing in the first fluid passage; and (b) a second fluid passage to the flow rate control valve that comprises at least one third fluid passages arranged in parallel, wherein the at least one third fluid passage is provided with a laminar flow element and a switching valve, wherein each laminar flow element has a different coarseness from the other, and fluid flowing in a small flow quantity range is made to flow to one laminar flow element that controls flow rate of fluid flowing in the small flow quantity range while fluid flowing in the large flow quantity range is made to flow to the other laminar flow element that controls flow rate control of fluid flowing in the large flow quantity range, wherein when fluid is flowing in the large flow quantity range each switching valve in the at least one third fluid passage are made to be open.
 11. A flow rate range variable type flow rate control apparatus comprising: (a) a thermal type mass flow rate control apparatus comprising (i) a flow rate control valve connected to a first fluid passage; (ii) a laminar flow element device part disposed on the first fluid passage; and (iii) a flow rate sensor part, wherein temperature changes in proportion to a mass flow rate of fluid are detected at the flow rate sensor part, and fluid with a predetermined set flow rate is made to flow out by opening or closing the flow rate control valve based on detected temperature of fluid flowing in the first fluid passage, wherein in response to receiving a flow rate setting signal, the thermal type mass flow rate control apparatus is switched to a flow rate setting suitable for a large flow quantity, a medium flow quantity or a small flow quantity setting; and (b) a second fluid passage to the flow rate control valve that comprises at least one third fluid passage arranged in parallel, wherein each third fluid passage is provided with a laminar flow element and a switching valve, wherein each laminar flow element has a different coarseness from the other, and fluid flowing in a small flow quantity range is made to flow to one laminar flow element that controls flow rate of fluid flowing in the small flow quantity range while fluid flowing in the large flow quantity range is made to flow to the other laminar flow element that controls flow rate control of fluid flowing in the large flow quantity range. 